Electrocardiographic and electrophysiologic studies in patients with torsades de pointe--role of monophasic action potentials.
The study group consisted of 26 patients with a history of documented Torsade de Pointes (TdP) who were divides into 3 groups according to the causes of TdP. Group I consisted of 5 patients with congenital long QT syndrome. Group II consisted of 15 patients with TdP caused by antiarrhythmic drugs. Group III consisted of 6 patients with TdP caused by bradycardia resulting from third degree atrioventricular block. The QT interval was determined from a 12-lead electrocardiogram. Monophasic Action Potential (MAP) was recorded by a 6 F USCI electrode catheter. Isoproterenol infusion resulted in TU abnormality in all patients in Group I and induced a hump at phase 3 slope of MAP in all 3 patients tested. The QT interval change before and after IA administration was significantly larger in Group II patients compared to those without TdP (0.132 +/- 0.062 vs 0.029 +/- 0.31 sec, less than 0.005). Injection of 100 mg. of disopyramide in 2 patients in Group II resulted a hump at phase 3 slope of the MAP in both of them. The QT prolongation associated with decreasing the pacing rate from 70 to 50/min was significantly larger in patients with Group III compared to patients with bradycardia but without TdP (0.02 +/- 0.04 vs 0.07 +/- 0.05 sec, p less than 0.005). The results suggests: 1) different approaches are necessary for evaluation of TU abnormalities in patients with TdP according to the causes of TdP, 2) MAP might be a useful method for evaluating TU abnormality in patients with TdP.
Ohe
T
T
Division of Cardiology, National Cardiovascular Center, Osaka, Japan.
Kurita
T
T
Aihara
N
N
Kamakura
S
S
Matsuhisa
M
M
Shimomura
K
K
D000200:Action Potentials; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000889:Anti-Arrhythmia Agents / Q000627:therapeutic use; D001919:Bradycardia / Q000150:complications; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006321:Heart / Q000503:physiopathology*; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008133:Long QT Syndrome / Q000150:complications / Q000151:congenital; D008297:Male; D008875:Middle Aged; D016171:Torsades de Pointes / Q000209:etiology / Q000503:physiopathology*
D000889:Anti-Arrhythmia Agents; D007545:Isoproterenol